A water-hydraulic machine of this kind is known from the “Nessie” project of Danfoss A/S, Nordborg, Denmark. An example of a publication of such a machine exists in DE 43 01 124 A1.
In a water-hydraulic machine, water is used as a hydraulic medium. Compared with the normally used hydraulic oils, water has the advantage that leakages causes practically no pollution of the environment.
However, water has the disadvantage that, contrary to oil, it has no lubricating properties. In a water-hydraulic machine, this usually leads to problems, as mutually movable parts cannot be lubricated and cooled to a sufficient extent.
Therefore, in the Nessie project mentioned above, when working with pairings of two mutually movable parts, one part has been provided with a layer or an insert of a plastics material, which is made of a friction-reducing plastics material. A preferred plastic material for this purpose comes from the group of high-performance thermoplastic plastics materials on the basis of polyarylether ketones, in particular polyetherether ketones (PEEK). Basically, the use of PEEK has turned out to be successful. Water-hydraulic machines provided with such a plastics material on the contact surface of mutually movable parts could also be operated reliably with water over long periods.
However, in one specific application, problems sometimes occur, when demineralised water is used as hydraulic fluid. Such applications comprise, for example, systems working according to the principle of reverse osmosis. As soon as “pure” water is used, wear phenomenon occur on mutually moving parts, particularly, when these parts are provided with PEEK.
The invention is based on the task of enabling operation of a water-hydraulic machine also with demineralised water.